1. Victims were older, usually over 60.
2. Victims were overweight.
3. Victims led inactive lives.
4. Victims were alcoholics.
5. Women were more prone to spontaneously combust than men.
6. At the scene there was often an external flame, such as a candle or fireplace.
7. Combustion was extremely rapid.
8. The flames were difficult to extinguish.
9. The flames produced a strong empyreumatic odor.
10. The surrounding room was coated with a thick, yellow, greasy film.
11. The first usually consumed the trunk of the body, but left the head and extremities intact.
12. Accidents occurred during fair weather, and more often in winter than in summer.

The factor of alcoholism was particularly significant, especially for members of the Temperance movement. In the 18th century, there were anecdotal reports of women who allegedly died as a result of spontaneous combustion who were known to be heavy drinkers, and in the 19th century, it wasn't uncommon to fear that the perennially soused might meet a fiery end. Prohibition advocates even listed spontaneous human combustion as one of the potential evils of alcohol.

The Lapham's Quarterly article has a fascinating account of some of the 18th century reports of spontaneous human combustion as well as more details on the relationship between these reports and the Temperance movement. It's also rather fascinating to compare this list to more recent attempts to determine whether the phenomenon is real or possible. One recent study suggested that ketosis might make the human body more flammable—and noted that alcoholism is a condition that can produce ketosis. But I can't help but wonder whether burning the body of someone who fit the accepted risk factors for spontaneous combustion might not have been a terrible way to cover up a murder.